sos: postgresql: align with upstream master

re-sync with upstream sos postgresql plugin, including
https://github.com/sosreport/sos/commit/7cdc1deabaeae226b498da74e1f60302f8a68a26
from Bryn M. Reeves.

Change-Id: I56129de7f208275495e4643444b3c522cec6aada
Signed-off-by: Sandro Bonazzola <sbonazzo@redhat.com>